Apparatus and method for measuring the heating of gases

ABSTRACT

A heating value meter for gases has an outer cylindrical mantle with an outer thermostatic heating apparatus and at least one inlet for air and a test gas. The outer mandrel has an outer heating mantle and a bottom part containing an outer sensor of the outer thermostatic apparatus. A cylindrical measuring block is located coaxially inside the outer mantle and is equipped with an axially inserted internal sensor of an electrical long-distance thermometer of an internal thermostatic apparatus. The heating mantle, the outer sensor, an electrical heating block and an internal sensor, are interconnected via the thermostatic apparatus and are adjusted for maintaining a constant temperature by regulation of the input to the electrical heating block, or by the input to the heating mantle where, in addition, the measuring apparatus is connected by an electric lead to the electrical heating block.

TECHNICAL FIELD

The invention relates to a measurement of the heat of combustion ofgases, or the heating value of gases, especially it concerns meters fordetermination of the heat of combustion of heating gases whose heatingcapacity may vary during delivery to the customers, and thus continuousmonitoring is required. The invention relates to a metering method, too.

BACKGROUND ART

A great variety of instruments are used at the present time formeasurement of the heat of combustion of gases. The so-calledcompensation meters that in principle compensate the differences in theheat of combustion of the test gas through the heat produced in acompensation source whose energy input is measured are often used forcontinuous measurement. In a number of these meters, an electricallyheated block serves as the compensation source. In this case, the issuemust be solved of attaining an equilibrium state between the input ofheat from the compensation and test sources and the heat dissipationinto the environment. A possible solution to this problem is describedin a patent CH 593484 where the test and compensation heat sources areplaced in the meter block that is connected to the cooling block bymeans of a heat-conducting element and the heat gradient between themeasuring and cooling blocks is maintained constant and measured. Theouter mantle around the measuring block is a part of the thermalinsulation preventing heat dissipation into the environment alongpathways other than that via the heat-conducting element. Such ameasuring instrument is suitable for determining the heating capacity ofa stable source placed in the measuring chamber but is less suited tocontinuous measurement of the heat of combustion of gases, where the gaspasses through the measuring space and where it would be difficult tothermally insulate the measuring space. Another solution can be seen ina patent SU 1160294, where gases pass through the measuring chamberwhich is neighbouring to the compensation chamber and where the twochambers are interconnected by a heat-conducting material while theouter mantle of the meter is equipped with ribs for heat dissipationunder which semiconductor thermo batteries are placed. This design isadapted for gas passage but it seems that this system combiningcontrolled heat dissipation across thermo batteries and cooling ribs andthermal insulation of the remaining surface of the outer mantle, israther complicated and it might be difficult to practically attain rapidand sufficiently sensitive regulation of heat dissipation. Furtherpatents, SU 1286979, 1288567, 1390557, 1402894, 1420496, 1430849,1430850, 1430851, 1492254 and 1492255, include attempts to compensatethe above drawbacks of instruments of similar types by modifying thearrangement of the measuring and compensation chambers and by addingfurther heating blocks.

DISCLOSURE OF INVENTION

The drawbacks of the instruments described above are substantiallyreduced and precise measurement of the heating value of gases isattained by a relatively technically simple instrument when usingheating value meter for gases according to the present invention thatconsists of an outer mantle with thermostatically controlled heating andat least one inlet for air and for the test gas, and of a measuringblock located inside the outer mantle, where the principle of the meterlies in the fact that the outer mantle is cylindrical and provided witha heating mantle on its outside surface, and that its bottom partcontains an axially placed outer sensor of an electrical long-distancethermometer of the outer thermostatic apparatus, and, simultaneously,the measuring block is cylindrical, with an axially placed through-hole,is placed coaxially inside the outer mantle and is provided in the upperpart with an axially-inserted internal sensor of an electricallong-distance thermometer of the internal thermostatic apparatus, whilethe heating mantle and the outer sensor and the electrical heating blockand the internal sensor are simultaneously interconnected across thethermostatic apparatus adjusted for maintaining a constant temperatureby regulating the input of the electrical heating block or of the inputof the heating mantle where a meter of the electric input is alsoconnected. It could be advantageous when both the outer mantle and themeasuring block of the meter of the heat of combustion of gases are madeof a metallic material, with especial advantage of an alloy based oncopper or aluminium. It is also advantageous when there is a gap betweenthe outer surface of the measuring block and the internal surface of theouter mantle, with a width equal to 0.3 to 3.0 fold the outer diameterof the measuring block. It is also an advantage if the overallcross-section of the outlets of the flue gases equals 1.1 to 2.0 foldthe overall cross-section of the air inlets. It is further advantageousif there are at least two air inlets in the outer mantle and if they aredirected at an angle and/or are diverging from the longitudinal axis ofthe measuring block. It is advantageous, too, if the electrical heatingblock and/or the internal sensor are placed closer to the circumferenceof the measuring block than to its axial through-hole. It is alsoadvantageous if a cavity is created or a shielding body made of athermally insulating material placed between the electrical heatingblock and/or the internal sensor, and the axial through-hole. Finally,it may be advantageous if the internal thermostatic apparatus isadjusted for regulation of the electrical input to the electricalheating block within a range from 5 to 50% of the heating capacity ofthe calibration gas combusted in the meter. Another principle underlyingthe invention is the mode of operation of the meter that involves firsta calibration stage consisting of feeding the a calibration gas with anexactly known heating capacity to the meter and of its combustion,followed by measurement of the temperature of the internal sensor andstorage of the value in the memory of the measuring apparatus, andsubsequently a measuring stage in which the test gas is introduced intothe meter and combusted while the measuring apparatus measures theelectrical input to the electrical heating block, the internalthermostatic apparatus maintains the measuring block temperature,measured at the internal sensor, at the same values as those obtainedand stored in the memory during the calibration stage, and the value ofthe heat of combustion of the test gas is determined from the differencebetween the value of the heating capacity of the calibration gas andthat of the electrical heating block, maintaining the temperature of theouter mantle at the same and constant value during the calibration andmeasuring stage. It is favourable to repeat the calibration stage every30 to 300 minutes.

In this way a meter is obtained that is relatively simple and stillreliably measures the heat of combustion of gases with a commonprecision of around 1%, or even better.

BRIEF DESCRIPTION OF DRAWINGS

Below, the invention is more closely explained and described on apreferred embodiment, with reference to the accompanying drawings inwhich FIG. 1 is the vertical cross-section through the measuringinstrument and FIG. 2 is the scheme of the connection of the measuringinstrument in the measuring system, with a connection to the pipelinetransporting the test gas.

MODES FOR CARRYING OUT THE INVENTION

The meter 1 consists of the outer mantle 10 provided with the heatingmantle 101, here designed as an electrical resistor heating mantle, withthe measuring chamber 11 placed inside the outer mantle 10. The outermantle 10 is an aluminium cup-shaped case closed with a lid at thebottom. The bottom lid contains the inlets 103 for air and the test orcalibration gas. The present example has two inlets 103 for air,perpendicular to the lid plane and between them, in the middle of thelid, is the inlet 105 for the test or calibration gas, which is parallelwith the air inlets 103. The outer temperature sensor 102 is placedaxially at the bottom edge of the cup-shaped case. The outer temperaturesensor 102 is connected to the outer thermostatic apparatus 2 which isfurther connected to the heating mantle 101. The outer thermostaticapparatus 2 also contains an energy source, or can be connected to anexternal energy source which is not depicted here. The centre of theupper part of the outer mantle 10 contains the outlet 104 for the fluegases, the ratio between the cross-section of the outlet 104 and theoverall cross-section of the air inlets 103 being 1.3, while the gapbetween the outer surface of the measuring block 11 and the internalsurface of the mantle 10 equals the outer diameter of the measuringblock 11. The measuring block 11 is designed as a hollow cylinder madeof aluminium, where the axial hole 113 in the measuring block has adiameter corresponding to that of the outlet 104 for the flue gases andis directed at the top toward the outlet 104. In the axial direction,close to the axially directed hole 113, the thermally insulating holes114 are made in the bottom and top planes of the measuring block 11,while the hole containing the internal temperature sensor 112 is made inthe bottom plane in the same direction but closer to the outercircumference of the measuring block 11 and the hole containing theelectrical heating block 111 is made in the upper plane. The internaltemperature sensor 112 is interconnected with the internal thermostaticapparatus 3 that is further connected, via the measuring apparatus 31 ofthe electrical input, to the electrical heating block 111. The measuringapparatus 31 is then connected to the evaluating and control unit 4 thatis based on a computer and is simultaneously connected to the firstdosing unit 41 for the calibration gas and the second dosing unit 42 forthe test gas.

The equipment according to the invention operates as follows. First, thecalibration stage takes place, i.e., the calibration gas with aprecisely known heating capacity, or heating value, is introduced intothe meter 1 and is combusted in it, followed by measurement of thetemperature at the internal sensor 112 and the storage of the value inthe memory of the measuring apparatus, and then the measuring stagetakes place, involving introduction of the test gas into the meter 1,its combustion in the meter, with measurement of the electrical input tothe electrical heating block 111 by the measuring apparatus andsimultaneous maintaining, by the thermostatic apparatus 3, of thetemperature of the measuring block 11 measured at the internal sensor112 at the same value as that determined and stored in the memory duringthe calibration stage; the value of the heat of combustion of the testgas is then determined from the difference between the value of theheating capacity of the calibration gas and that of the heating capacityof the electrical heating block, while the temperature of the outermantle 10 is maintained at the same and constant value, by means oftemperature measurement using the outer sensor 102 and subsequentregulation of the heating capacity of the electrical heating block 111,with regulation by the outer thermostatic apparatus 2. The calibrationstage is repeated every 30 minutes during the measuring process, while 6measurements of the heat of combustion value of the test gas are carriedout per hour which, in view of the present requirements, can beconsidered to be continuous measurement. The equipment described abovepermitted measurements with a precision characterized by deviations notexceeding 1% from the precise value of the heating value verified bylaboratory measurements and by control with other calibration gases.

In view of the computer control and monitoring of the measuring process,there is no problem in creating, basically by software means, theso-called thermal fuse which normally closes the gas inlet to heatingsystems when the gas supply is interrupted, to prevent explosion orpollution by non-ignited gas on resuming the supply. Here an error andalarm signal is generated when the control unit 4 records that theheating capacity of the compensation electrical heating block 111 nolonger suffices for the compensation of the decreasing heating capacityof the test gas in the measuring block 11, i.e., that the combustion inthe measuring block 11 was actually interrupted. The inlet of gases isthen closed and the instrument requires intervention by the personnel.

As far as continuity of measurement is concerned, measurement can beconsidered continuous, except for the calibration stages. However, theseinterruptions do not prevent calling the measurement continuous, as thepresent-day criteria for continuous measurement require that at least 6measurements be performed per hour. The equipment described here permitsat least 6 measurements per hour without any problem, with a calibrationfrequency of up to every 30 minutes, including the periods of timerequired for temperature establishment and stabilization in themeasuring apparatus 1, after the calibration stages.

INDUSTRIAL APPLICABILITY

The equipment according to the invention can be used for any measurementof the heating value of combustible gases, however, it is especiallysuitable for continuous, fully automated measurements of the heatingvalue of natural gas and of similar heating gases for which suchmeasurement is required according to the present invoicing regulations.Understandably, the equipment is equally readily applicable to both thesubstances in the gaseous state that are designated as gases and thosedesignated as vapours.

1. The heating value meter for gases, consisting of an outer mantle withthermostatically controlled heating and with at least one inlet for airand the test gas, and a measuring block placed inside the outer mantle,characterized in, that outer mantle (10) is cylindrical, it is equippedwith a heating mantle on its outer surface (101) and its bottom partcontains an outer sensor (102) of an electrical long-distancethermometer of the outer thermostatic apparatus (2) placed axially inthe wall, and a measuring block (11) is also cylindrical with an axialthrough-hole (113), it is located coaxially inside the outer mantle (10)and its upper part is equipped with an axially inserted internal sensor(112) of an electrical long-distance thermometer of the internalthermostatic apparatus (3), while the heating mantle (101) and the outersensor (102), and also the electrical heating block (111) and theinternal sensor (112), are interconnected via the thermostatic apparatus(2,3), adjusted for maintaining of a constant temperature value byregulation of the input to the electrical heating block (111), or of theinput to the heating mantle (101) where, in addition, the measuringapparatus (31) of the electrical input is connected to the electric leadto the electrical heating block (111).
 2. The heating value meter forgases, according to claim 1, characterized in, that the outer mantle(10) and the measuring block (11) are made from a metallic material. 3.The heating value meter for gases, according to claim 1 characterizedin, that the outer mantle (10) and the measuring block (11) are madefrom an alloy based on copper or aluminium.
 4. The heating value meterfor gases, according to claim 1, characterized in, that a gap existsbetween the outer surface of the measuring block (11) and the internalsurface of the outer mantle (10), with a width equal to 0.3 to 3.0 foldthe outer diameter of the measuring block (11).
 5. The heating valuemeter for gases, according to claim 1, characterized in, that theoverall cross-section of the outlets (104) for the flue gases equals 1.1to 2.0 fold the overall cross-section of the air inlet (103).
 6. Theheating value meter for gases, according to claim 1, characterized in,that there are at least two air inlets (103) in the outer mantle (10)and that they are bored at an angle or are diverging from thelongitudinal axis of the measuring block (11).
 7. The heating valuemeter for gases, according to claim 1, characterized in, that theelectrical heating block (111) and/or the internal sensor (112) areplaced in the measuring block (11) closer to its circumference than toits axial through-hole (113).
 8. The heating value meter for gases,according to claim 1, characterized in, that a cavity (114) is formedbetween the position of the electrical heating block (111) and/or theinternal sensor (112), and the axial through-hole (113), and/or ashielding body (115) made of a thermally insulating matter is placed inthe cavity position.
 9. The heating value meter for gases, according toclaim 1, characterized in, that the internal thermostatic apparatus (3)is adapted for regulation of the electrical input to the electricalheating block (111), within a range from 5 to 50% of the heatingcapacity of the calibration gas combusted in the meter (1).
 10. Themethod of operation of the heating value meter constructed according toclaim 1, characterized in, that first the calibration stage takes placeinvolving introduction and combustion of a calibration gas with aprecisely known heat of combustion in the meter (1), followed bymeasuring the temperature value at the internal sensor (112) and storingit in the memory of the measuring apparatus, followed by the measuringstage consisting of introduction and combustion of the test gas in themeter (1), with simultaneous measurement, by means of the measuringapparatus (31), of the electrical input to the electrical heating block(111) and maintaining, by means of the internal thermostatic apparatus(3), the temperature of the measuring block (11) measured at theinternal sensor (112), at the same value as that determined and storedin the memory during the calibration stage, and the value of the heat ofcombustion of the test gas is determined from the difference between theheat of combustion value of the calibration gas and the value of theheating capacity of the electrical heating block (111), keeping theouter mantle (10) temperature at the same and constant value during thecalibration and measuring stages.
 11. The method of operation, accordingto claim 10, characterized in, that the calibration stage is repeatedevery 30 to 300 minutes during the measuring process.